1. Field of the Invention
This invention relates to the recovery of mineral values from subterranean formations and more particularly to a process for leaching subterranean mineral deposits to recover mineral values therefrom.
2. Description of the Prior Art
Solution mining involves the in situ leaching of mineral values from a subterranean mineral-bearing formation. Typically a leaching solution is injected through a well into the formation to solubilize the desired mineral values and thereby form a pregnant liquor. The pregnant liquor is then recovered and treated to separate the mineral values therefrom. An oxidant may also be injected into the formation to aid in solubilizing mineral values which are only soluble, or are more readily soluble, in an oxidized form.
In the conventional solution mining process, the leaching solution is injected continuously into the mineral-bearing formation through one or more injection wells and the pregnant liquor is recovered continuously through one or more production wells. The rate of mineral recovery, and perhaps the ultimate mineral recovery, may be increased by changing the direction of flow through the formation by converting one or more of the injection wells to production wells and vice versa, thereby reversing the direction of flow through the formation, or by shutting in the initial injection wells and converting some of the production wells to injection wells, thereby forcing leaching solution through previously unleached portions of the formation. In any event, the injection-and-production phase is normally continued until the mineral-bearing formation is exhausted of the desired mineral values or, as a practical matter, until further operations become uneconomical.
After the injection-and-production phase has been completed, it may be desirable to restore the mineral-bearing formation and the ground water contained therein to substantially their pre-leach condition. Typically, the restoration operation will include a production-only phase during which ground water is pumped out of all of the wells employed in the solution mining operation to thereby remove any remaining leaching solution and/or oxidant. After completion of the production-only phase, the wells are generally abandoned.
The cost of the chemicals employed in a particular solution mining process and the cost of restoring the subterranean mineral-bearing formation to its pre-leach condition are major factors in determining the economic viability of that process. The solution mining processes disclosed in my U.S. Pat. No. 4,105,253 and my copending applications Ser. No. 894,936, filed Apr. 10, 1978 and Ser. No. 903,257, filed May 5, 1978 result in a substantial reduction in these costs as compared to other solution mining processes. However, further cost reductions are desirable.
Accordingly, it is a primary object of this invention to provide an improved method for the solution mining of mineral values from subterranean formations in which the chemical costs and costs of formation restoration are substantially reduced.
Another object of this invention is to provide an improved solution mining process in which the rate of recovery and the ultimate recovery of the desired mineral values are increased while at the same time the cost of the solution mining process is reduced.
Further objects, advantages and features of the invention will become apparent to those skilled in the art from the following description when taken in conjunction with the accompanying drawings.